Process and Installation for Producing a Component from Sheet Magnesium

ABSTRACT

The invention relates to a method and an installation for producing a component from sheet magnesium, comprising a forming tool, which comprises a punch and a die, for forming a semi-finished product made of sheet magnesium, in particular a semi-finished product in the form of a sheet magnesium blank, and a device for heating the semi-finished product to an elevated temperature, preferably to a temperature of at least 200° C., prior to the forming. In order to reduce the component costs, the invention proposes that the forming tool is designed without an internal heat source, is provided with a semi-finished product holder on which the heated semi-finished product can be placed in the forming tool without direct contact with the punch and the die, and comprises a drive which brings about a closing speed of the punch and the die in the range of 15 mm/s to 500 mm/s.

The invention relates to a method for producing a component from sheetmagnesium by forming a semi-finished product made of sheet magnesium, inparticular a semi-finished product in the form of a sheet magnesiumblank, in which the semi-finished product is heated to an elevatedtemperature, preferably to a temperature of at least 200° C., prior tothe forming and is formed in a forming tool comprising a punch and adie. The invention further relates to an installation for producing acomponent from sheet magnesium.

Owing to the hexagonal lattice structure of magnesium, magnesium sheetscan only be formed with difficulty at room temperature. In particular,components made of sheet magnesium which are to have a complexthree-dimensional shape must be hot formed to avoid cracks. In general,magnesium blanks are formed in the heated state using tempered tools.

In the prior art, various configurations of tempered tools for formingmagnesium sheets are known. For example, Korean patent application 102006 00 57 901 A discloses a press for hot forming sheet magnesium,which press is provided with an electric resistance heating device. Inthis case, the resistance heating device is integrated in an upper toolpart (die) and in an associated sheet holder.

In comparison with conventional tools used in cold forming, temperedforming tools involve a higher level of technical complexity and thushigher investment and higher operating costs. This has a negative impacton the costs of components made of magnesium.

The object of the present invention is to provide a method and aninstallation for producing a three-dimensional component from sheetmagnesium which allow low component costs.

According to the invention, this object is achieved by a method havingthe features of claim 1 and by an installation having the features ofclaim 9.

The method according to the invention is characterised in that a formingtool designed without an internal heat source being used for forming thesemi-finished product heated to an elevated temperature, preferably to atemperature of at least 200° C., the heated semi-finished product beingplaced in the forming tool without direct contact with the punch and thedie and is then formed at a forming speed in the range of 15 mm/s to 500mm/s.

The installation according to the invention is accordingly characterisedin that the forming tool thereof being designed without an internal heatsource and being provided with a semi-finished product holder on whichthe semi-finished product heated to an elevated temperature, preferablyto a temperature of at least 200° C., can be placed in the forming toolwithout direct contact with the punch and the die, and comprising adrive which brings about a closing speed of the punch and the die in therange of 15 mm/s to 500 mm/s.

Owing to the present invention, the additional complexity caused by thetempering of the forming tool by means of an internal heat source doesnot apply. The invention provides for the processing of a heatedmagnesium semi-finished product in a forming tool without an internalheat source.

The tool and operating costs and thus ultimately the component costs arereduced considerably as a result, In particular when producingcomponents in relatively small quantities, the profitability of thecomponent can be increased substantially owing to the reduction of thetool costs.

Through tests, the inventors were able to show that athree-dimensionally shaped component can be produced without cracks froma magnesium blank, which for example is heated to 250° C., in anuntempered forming tool when excessive temperature losses are avoidedprior to the actual forming process by preventing the heated plate frombeing deposited directly'on the punch or the die when the blank isplaced (laid) in the forming tool, and the subsequent forming takesplace at a relatively high forming speed (15-500 mm/s).

The average cooling speed for a 2.00 mm thick magnesium sheet which isheated to a temperature in the range of 200° C. to 250° C. is, forexample in air at room temperature of 20° C., between 2 and 12 K/s.Owing to this relatively small temperature loss, it can be ensured in asuitable transfer system that the heated semi-finished product or theheated blank has, prior to the forming, a sufficiently high startingtemperature to allow a error-free, in particular crack-free componentwith given degrees of deformation.

The use according to the invention of an untempered tool for formingheated magnesium blanks also has positive effects with regard to thedimensional accuracy and the handling of the components produced in thismanner. This is because, owing to the considerably reduced temperaturewhich the component has when it is removed from the untempered formingtool, the component has greater dimensional stability in comparison witha component produced in a tempered tool and is thus less susceptible toundesired deformations when it is removed from the forming tool andduring subsequent handling, and this has a positive effect on thedimensional accuracy of the component. In addition, the componentsproduced according to the invention are easier to handle owing to theconsiderably reduced temperature which they have when they are removedfrom the untempered forming tool. In this case, conventional transfersystems can be used which are not temperature-stable or havecomparatively low temperature stability.

In this context, an advantageous configuration of the method accordingto the invention provides that, as a forming tool, a forming tool isused in which the punch and/or die comprise an active cooling apparatus.As a result, the removal temperature of the component can be loweredmore rapidly, the dimensional accuracy of the component can be improvedfurther and the handling of the component can be simplified further.This active cooling of the punch and/or the die is advantageous inparticular when comparatively large quantities are to be formed in apredetermined time, that is to say when the desired forming capacity isto be relatively high. However, heating of the forming tool owing to theheated semi-finished product during production can also be toleratedwhen there are no negative effects on the dimensional accuracy of thefinished component as a result.

An advantageous configuration of the invention, allowing that the heatedsheet magnesium semi-finished product must not deposited directly on thepunch or the die, consists in that the heated semi-finished product isplaced on a semi-finished product holder associated with the formingtool, and therefore the essential surface region of the heatedsemi-finished product is arranged in a self-supporting manner in theambient atmosphere between the punch and the die and with spacingtherefrom prior to the actual forming process. In this case the ambientatmosphere, preferably ambient air, acts as a heat insulator. Thisensures that the heated semi-finished product undergoes only very slightcooling prior to the actual forming process. In this case thesemi-finished product holder is designed, for example, as an activesheet holder which is positioned above a punch associated with the die.

Another advantageous configuration of the method according to theinvention is characterised in that, as a semi-finished product holder, asemi-finished product holder is used, the surface region of whichtouching the heated semi-finished product has a surface structure whichis porous or comprises indentations. This reduces the heat ortemperature loss of the heated semi-finished product caused byconduction of heat from the heated semi-finished product to thesemi-finished product holder.

Additionally or alternatively, another advantageous configuration of themethod according to the invention provides that, as a semi-finishedproduct holder, a semi finished product holder is used, the surfaceregion of which touching the heated semi-finished product is made of amaterial, or is provided with a coating, which has a thermalconductivity of at most 20 W/mK at 30° C. to 100° C. ambienttemperature. This, too, reduces the heat or temperature loss caused byconduction of heat from the heated semi-finished product to thesemi-finished product holder.

Another advantageous configuration of the method according to theinvention is characterised in that, as a die, a die is used which has,in its forming face which faces the heated semi-finished product to beformed, indentations which bring about a reduction of the contact facewhich faces the heated semi-finished product. The indentations or theair contained therein has/have a heat-insulating effect, and thereforethe heat or temperature loss of the heated semi-finished product can bereduced in this manner.

Another advantageous configuration of the method according to theinvention provides that the semi-finished product is transporteddirectly into the forming tool by means of a transfer device which isprovided with a conductive heat source. As a result, the semi-finishedproduct to be formed can be given a sufficiently high startingtemperature prior to the forming and at the same time the temperatureloss of the semi-finished product prior to the forming can be minimised.

Owing to the use of an untempered forming tool, cost-effectiveintegrated component trimming during the forming of the semi-finishedproduct which consists of sheet magnesium is also conceivable. Anotheradvantageous configuration of the method according to the invention isaccordingly characterised in that, during the forming, the semi-finishedproduct is simultaneously trimmed by means of at least one cuttingmember integrated in the forming tool.

Other preferred and advantageous configurations of the installationaccording to the invention are given in the dependent claims.

The invention will be described in detail below with reference todrawings showing a plurality of embodiments, in which:

FIG. 1 shows schematically an installation or a process line forproducing three-dimensionally shaped components from magnesiumsemi-finished products;

FIG. 2 shows schematically another embodiment of a process line forproducing three-dimensionally shaped components from magnesiumsemi-finished products; and

FIG. 3 is a schematic vertical sectional view of a forming toolaccording to the invention.

The installation shown in FIG. 1 basically comprises a device 1 forheating a semi-finished product 2 made of sheet magnesium and a formingtool 3, without an internal heat source, for forming the heatedsemi-finished product 2. The semi-finished product 2 to be formed mayfor example be in the form of a sheet magnesium blank.

In this case, the device 1 for heating the semi-finished product 2 isdesigned as a continuous furnace, preferably as a roller hearth furnace.The continuous furnace or roller hearth furnace 1 is provided withinductors, radiant heaters, hot-air burners and/or recuperator burners.It is also conceivable to use infra-red radiators to heat thesemi-finished product 2 to be formed.

In the embodiment shown, sheet magnesium blanks 2 to be formed areremoved from a conveyor belt or a supply stack 4 and heated in thecontinuous furnace 1 to an elevated temperature which is selected suchthat the workpiece temperature is substantially still above 180° C. to220° C. at the end of the forming. For this purpose, the sheet magnesiumblank or the semi-finished product 2 is heated for example to atemperature in the range of 230° C. and 260° C.

The heated semi-finished product 2 is then grasped by means of atransfer device 5, preferably a robot, in the region of the outlet ofthe continuous furnace and laid in the forming tool 3 without directcontact with the punch 3.1 and the die 3.2. For this purpose the formingtool 3 is provided with a semi-finished product holder (sheet holder)3.3 which, when the forming tool 3 is open, is positioned above thepunch head, such that the semi-finished product 2 deposited thereontouches neither the punch 3.1 nor the die 3.2. In FIG. 1 it can be seenthat the blank 2 placed in the forming tool is initially deposited onthe semi-finished product holder 3.3 and is arranged with spacing fromboth the punch 3.1 and the die 3.2. This prevents excessively rapidcooling of the heated sheet magnesium blank 2.

The tool 3 is then closed in order to form the heated semi-finishedproduct into a shape which is predetermined by the punch 3.1 and the die3.2. The forming takes place at a relatively high forming speed, suchthat the temperature loss of the heated workpiece (semi-finishedproduct) 2 during the forming is also kept low. In order to achieve acorrespondingly high forming speed, the forming tool 3 comprises a drive(not shown) which brings about a closing speed of the punch 3.1 and die3.2 in the range of 15 mm/s to 500 mm/s.

After the forming tool 3 is opened, the component 2′ produced in thismanner is removed from the forming tool 3 by means of a suitabletransfer device 6, preferably a robot, and optionally deposited orstacked on a transport means, for example a transport plate or the like.

Should the temperature loss be too high for the component geometry orthe degree of deformation owing to the use of conventional tool steels,the tool 3 can, at least in sub-regions, consist of materials havingrelatively low thermal conductivity and/or have a coating which has lowthermal conductivity. Besides ceramic materials, special tool steels canalso meet these requirements. For example, the punch 3.1 and/or the die3.2 of the forming tool 3 can, at least in sub-regions, be made of amaterial which has a thermal conductivity of at most 20 W/mK at 30° C.to 100° C. ambient temperature. Alternatively, the thermal conductivitycan also be reduced by means of a suitable coating.

Another preferred configuration of the installation according to theinvention involves the surface region 3.31 of the semi-finished productholder 3.3, which surface region touches the heated semi-finishedproduct 2, having a surface structure which is porous or comprisesindentations 3.32. This further reduces the temperature loss of theheated semi-finished product 2. Additionally or alternatively, it isprovided that the surface region 3.31 of the semi-finished productholder 3.3, which surface region touches the heated semi-finishedproduct 2, is made of a material which has a relatively low thermalconductivity, or is coated with such a material. The thermalconductivity of the material used for the semi-finished product holder3.3 or of a coating used for the semi-finished product holder 3.3 ispreferably at most 20 W/mk at 30° C. to 100° C. ambient temperature.

FIG. 2 shows another embodiment of an installation according to theinvention for producing a three-dimensionally shaped component 2′ fromsheet magnesium. This installation differs from the installationaccording to FIG. 1 in that a sheet magnesium blank 2 to be formed isheated not in a continuous furnace but in or by means of a robot-liketransfer device 5′. For this purpose, the transfer device 5′ is providedwith a heating apparatus or conductive heat source 5.1 such that themagnesium sheet 2 is heated while it is being transported from a supplystack 4 or a conveyor belt into the forming tool 3. In this case, theconductive heat source or heating apparatus 5.1 is integrated intogripping or holding members of the transfer device 5′, by means of whichmembers the magnesium sheet (semi-finished product) 2 is gripped andtransported to the forming tool 3 and deposited therein.

The forming tool 3 in the installation shown in FIG. 2 is designed asper the forming tool 3 in the installation according to FIG. 1, andtherefore reference is made in this respect to the above description ofFIG. 1 in order to avoid repetition.

The installations shown schematically in FIGS. 1 and 2 are process lineswhich operate substantially continuously. It is not shown that it isalso possible to work off a coil, that is to say that the material iswound off a coil and, depending on the existing process line, eitherrectangular blanks are cut to length, for example when trimming takesplace during or after the forming, or shaped blanks, the contour ends ofwhich substantially correspond to specified sizes of the finishedcomponent.

FIG. 3 is a schematic vertical sectional view of a forming tool 3according to the invention which can be used for example in theinstallation according to FIG. 1 or 2. The forming tool, which is shownopen, again comprises a punch 3.1 and a die 3.2 for forming a sheetmagnesium blank 2. The forming tool 3 does not contain an internal heatsource. It is provided with a semi-finished product holder (blankholder) 3.3 on which the heated blank 2 can be placed without directcontact with the punch 3.1 and the die 3.2. The surface region 3.31 ofthe semi-finished product holder 3.3, which surface region serves as adepositing surface for the heated blank 2, is initially located abovethe punch 3.1 when the forming tool 3 is in the open, loading state. Thesurface region 3.31 of the semi-finished product holder 3.3 has asurface structure provided with groove-shaped recesses or indentations3.32. In addition, recesses or indentations 3.21 are also formed in thesurface of the cavity of the die 3.2, which cavity receives the punchhead. The recesses or indentations 3.32 and 3.21 define air gaps or airducts which have a heat-insulating effect and thus prevent rapid heat ortemperature loss of the heated blank 2. By contrast, the surface, facingthe blank 2, of the punch 3.1 which is moved into the cavity of the die3.2 in order to form the blank 2, does not comprise any indentationsforming air ducts, since in this case this punch surface is the actualshaping surface of the forming tool 3.

In order to keep the temperature of the component 2′ to be removed fromthe forming tool 3 low in the case of relatively large quantities ofcomponents 2′ to be produced from sheet magnesium, the punch 3.1 and/orthe die 3.2 can also be provided with an active cooling system (notshown). A cooling system of this type can be integrated in the punch 3.1and/or the die 3.2 for example by means of a crown construction and/orby means of cooling ducts.

1. A method for producing a component from sheet magnesium by forming asemi-finished product made of sheet magnesium in which the semi-finishedproduct is heated to an elevated temperature, prior to the forming andis formed in a forming tool comprising a punch and a die, wherein theforming tool used for forming the heated semi-finished product isdesigned without an internal heat source, the heated semi-finishedproduct is placed on a semi-finished product holder associated with theforming tool without directly contacting the punch and the die, thesemi-finished product holder is designed as an active sheet holder andis positioned above the punch associated with the die, and the heatedsemi-finished product placed on the semi-finished product holder is thenformed at a forming speed in the range of 15 mm/s to 500 mm/s. 2.(canceled)
 3. The method according to claim 1, wherein the semi-finishedproduct holder comprises a surface region that touches the heatedsemi-finished product and has a surface structure which is porous orcomprises indentations.
 4. The method according to claim 1, wherein thesemi-finished product holder comprises a surface region that touches theheated semi-finished product and is made of a material, or is providedwith a coating, which has a thermal conductivity of at most 20 W/mK at30° C. to 100° C. ambient temperature.
 5. The method according to claim1, wherein the die has, in its forming face which faces the heatedsemi-finished product to be formed, indentations which bring about areduction of the contact face which faces the heated semi-finishedproduct.
 6. The method according to claim 1, wherein a forming tool isused in which the punch, the die, or both comprise an active coolingapparatus.
 7. The method according to claim 1, wherein the semi-finishedproduct is transported directly into the forming tool by means of atransfer device which is provided with a conductive heat source.
 8. Themethod according to claim 1, wherein, during the forming, thesemi-finished product is simultaneously trimmed by means of at least onecutting member integrated in the forming tool.
 9. An installation forproducing a component from sheet magnesium, comprising a forming tool,which comprises a punch and a die, for forming a semi-finished productmade of sheet magnesium the forming tool being designed without aninternal heat source, and a device for heating the semi-finished productto an elevated temperature prior to the forming, wherein the formingtool further comprising a semi-finished product holder, designed as anactive sheet holder which can be positioned above the punch and on whichthe heated semi-finished product can be placed in the forming toolwithout direct contact with the punch and the die, and a drive whichbrings about a closing speed of the punch and the die in the range of 15mm/s to 500 mm/s.
 10. The installation according to claim 9, wherein asurface region of the semi-finished product holder, which surface regiontouches the heated semi-finished product, has a surface structure whichis porous or comprises indentations.
 11. The installation according toclaim 9, wherein a surface region of the semi-finished product holder,which surface region touches the heated semi-finished product, is madeof a material, or is provided with a coating, which has a thermalconductivity of at most 20 W/mK at 30° C. to 100° C. ambienttemperature.
 12. The installation according to claim 9, wherein thepunch, the die, or both of the forming tool, at least in sub-regions,are made of a material, or provided with a coating, which has a thermalconductivity of at most 20 W/mK at 30° C. to 100° C. ambienttemperature.
 13. The installation according to claim 9, wherein thepunch, the die, or both of the forming tool comprise an active coolingapparatus.
 14. The installation according to claim 9, wherein a transferdevice provided with a conductive heat source is associated with theforming tool, by means of which transfer device the semi-finishedproduct to be formed can be placed directly on the semi-finished productholder.
 15. The installation according to claim 9, wherein indentationswhich bring about a reduction of a contact face which faces the heatedsemi-finished product are formed in the die.
 16. The installationaccording to claim 9, wherein the forming tool is provided with at leastone cutting member.
 17. The method according to claim 1, wherein thesemi-finished product is a sheet of magnesium blank.
 18. The methodaccording to claim 1, wherein the semi-finished product is heated to atemperature of at least 200° C.
 19. The installation according to claim9, wherein the semi-finished product is a sheet magnesium blank.
 20. Theinstallation according to claim 9, wherein the device heats thesemi-finished product to a temperature of at least 200° C.